Because of the characteristics, such as all-weather, high-accuracy and automatic measuring, possessed by the global positioning system (GPS) technology, as the advanced measurement means and new productivity, it had already been integrated into various application fields, such as the national economic construction, the national defense construction and the social development.
Along with the end of cold war and the flourishing development of the global economy, the U.S. government announce to cancel the SA policy during the year 2000 to year 2006, on the premise of guaranteeing the U.S.A. national security not at risk, and the GPS civil signal precision is improved in the world wide, and the precision to locate the simple point by using the C/A code is raised to 10 meters from 100 meters, which will further promote the application of the GPS technology, raise the productivity, the working performance, the scientific level and the living quality of people, and stimulate the growth of the GPS market.
The main function of the assisted global positioning system (A-GPS) technology is to be able to provide the high-accuracy location information for the terminal user. After the mobile operator adopts the location service based on the A-GPS locating technology, the terminal user can know the current position of oneself or others conveniently and swiftly, which is especially suitable for the vehicle tracing and the navigation system and the vehicles with special tasks (armor cash carrier, ambulance, fire vehicle, etc.), and is able to increase the vehicle security, the transportation efficiency and the service quality by a large margin. At present, as the domestic mobile communication market is growing day by day, especially along with the coming of the commercial usage of 3G, China Mobile and China Unicom have all made and put out their own A-GPS schemes.
The product functions of the mobile terminals are more and more comprehensive at present, and most mobile terminals have the satellite positioning function, such as the GPS, the A-GPS, etc., and the user can know one's own location at any time. But the satellite locating module, such as the GPS module or the A-GPS module, needs to frequently read the location information along with the movement of the user and the constant change of the location, which leads to the problems, for example, the power consumption of the satellite locating module, such as the GPS module or the A-GPS module, is greater, the data updating will be delayed, etc.